1. Field of the Invention
The present invention relates generally to a wind energy conversion system and, more particularly, to the design and manufacture of a hybrid wind turbine system that can be designed to provide certain level of power during low wind speed seasons. The hybrid system uses the assistance of jet thrusters powered by liquid fuel or natural gas in a very economical manner with low investment.
2. Description of Prior Art
In recent years, wind energy projects have included the installation of large numbers of wind turbine generating systems at locations having favorable wind conditions. But, the practical turbines are not producing the amount of wind energy that was projected. There are many reasons for this shortfall of wind energy. Little can be done about the wind itself, with the exception of understanding the available resource better by using direct measurement and analysis. However, a new hybrid rotor system according to the present invention, designed to take better advantage of the available wind resource, provides an opportunity for a significant increase of energy production.
Albert Betz, a German engineer showed that the maximum energy that can be converted to electrical/mechanical energy in a stream of wind is less than 59%. But, a practical wind turbine, according to Paul Gipe, can only deliver less than 20% of the available power. The reason for such significantly low energy conversion efficiency may be attributed to the downstream velocity (V2) behind a single rotor being greater than one third of the upstream velocity (V1). Furthermore, according to C. G. Curtis, who is known for xe2x80x9cCurtis Stage Velocity Compoundingxe2x80x9d in steam turbine design, it is well known that a single stage wind rotor system cannot possibly extract the amount of power estimated by Betz.
A few patents are typical of the known prior art attempting to improve on earlier efforts to harness wind energy. For example, U.S. Pat. No. 5,456,579 to Olson discloses a wind turbine blade with a governor to maintain optimum rotational speed. The governor positions an aileron for varying wind speed and includes a lead weight positioned at the wing tip and connected to a mechanism that deploys the aileron to achieve the maximum lift to drag ratio at all wind speeds. U.S. Pat. No. 5,419,683 to Peace discloses a method of installing a plurality of wind turbines on chimneys, towers or the like. Two rotors having their horizontal axes are mounted back to back on a ring that turns about the chimney. The primary concept of this invention is to utilize existing structures to mount a plurality of wind turbines and to eliminate the need for wind farms. U.S. Pat. No. 4,976,587 to Johnston et al. discloses a method for manufacturing composite blades having highly improved aerodynamic efficiency. The blades employ the NASA airfoil section LS(1)-04XX having 29 per cent thickness at 3/10 radius and 18 per cent at the blade tip. The airfoil section comprises two spars, which terminate into a circular section at the hub. U.S. Pat. No. 4,648,801 to Wilson discloses a method of compressing air by means of a wind turbine. The air is drawn from the low energy region of the downwind stream. The compressed air is connected to the intake of a prime mover (such as a diesel engine, a gasoline engine, or a gas turbine) to boost its output power and drives an alternator. U.S. Pat. No. 6,127,739 issued to Appa discloses a jet assisted counter rotating wind turbine system designed to enhance power conversion efficiency utilizing blade tip mounted jet thrusters and counter rotation of tandem rotors. U.S. Pat. No. 5,660,038 issued to Joseph Walter Stone discloses a power generating Rotary Jet Engine that uses at least one combustion jet mounted on a circular disk. U.S. Pat. Nos. 6,223,521 and 6,233,918 issued to Shawn P. Lawlor disclose a method of power generation by means of a Ramjet Engine similar to that of U.S. Pat. No. 5,660,038. It was with knowledge of the foregoing state of the technology that the present invention has been conceived and is now reduced to practice.
The present invention describes a method of designing and manufacturing a hybrid wind turbine apparatus, which can provide certain level of power even when wind speed is as low as cut-in speed without requiring any auxiliary units. Said apparatus comprises:
1. a pair of counter rotating rotors having their blade angles set to rotate in opposite directions,
2. a pair of electrical power generating alternators placed in tandem and having their rotating magnetic field drums directly connected to said counter rotating rotors,
3. plurality of air breathing micro thrusters having one unit fitted to each blade tip in a sense to assist aerodynamic torque when needed,
4. a rotary fluid coupler to transfer natural gas or liquid fuel from a stationary platform to a rotating platform in a radial direction along a duct in each of the rotor blades,
5. a heat exchanger fitted with a centrifugal fan to cool the armature using incoming ambient air, and direct the hot air to the blade tip passing through ducts provided in each blade,
6. plurality of battery packs fitted to each blade and powered by plurality of solar cells fitted on to the surface of the blade near the tip sections,
7. plurality of gas sensors and igniters to sense incoming fuel and ignite fuel and air mixture,
8. a mast to support the wind turbine assembly and having a yaw bearing to align the rotors into the wind direction.
Wind turbines are designed to generate rated power at an average wind speed in a specific site. When the wind speed is far below the rated speed energy production will be negligible, since power varies as cube of the wind speed. For example, if the wind speed is half of the design speed, then the electrical power production will be 1/8th of the rated power. To supplement the loss of power, auxiliary power generating units such as gas turbine generators are required. This amounts to additional investment. And moreover operating cost will be high since gas turbines are less efficient. To circumvent the deficiencies of season dependent wind turbines, the present innovation suggests the use of inexpensive air breathing thrusters mounted at the tip of rotor blades to assist wind turbines when needed. A thruster may belong to any of the following class of air breathing engines such as micro gas turbines, rockets, ramjets, pulsejets or a combination of any of these devices. In essence a thruster must be mechanically simple, inexpensive to manufacture and maintain. Again, these must be able to use natural gas or any inexpensive fuel source to power these thrusters. The aerodynamic torque balances the rotor drag and mechanical friction whenever the wind speed is higher than the cut-in speed. Hence, any thrust imposed in the direction of the rotor rotation will do a useful work and generate electrical power at reduced cost of fuel used by the thruster.
Furthermore as discussed in the previous section, a single stage rotor system can not convert physically possible amount of wind power into electrical power. Therefore, the proposed invention suggests another improvement, a two-stage rotor device that is set to rotate in opposite directions. There are two ways to incorporate the counter rotating system. One approach is to use a single alternator, in which one rotor drives an armature, while the other rotor drives a drum of magnetic field having plurality of pole pairs. Thus, the magnetic flux rate in the air gap will be doubled resulting in higher voltage at lower rotational speed. The present inventor has already disclosed this approach in the U.S. Pat. No. 6,127,739.
Now we turn to an alternate approach, which comprises two sets of wind turbine units mounted in tandem such that their rotors rotate in opposite directions. In a counter rotating system the net torque is practically zero, if both machines produce same power. Hence it is possible and economical to upgrade existing wind machines using the same towers.
In essence, the proposed hybrid wind turbine device involves three distinct innovations. In a first instance, the turbine design of the invention comprises a pair of counter rotating rotors that are directly mounted on the generator units without using any mechanical gearing devices. Consequently, this reduces total weight of the system, initial unit cost and maintenance cost. More importantly, a dual rotor system is believed to extract substantially increased amount of power from the wind, and doubles the electrical voltage output resulting in reduced copper losses and cost.
In a second instance, thruster assisted hybrid power generating device reduces initial capital cost of power in terms of dollar per kilowatt. Because, thrusters are very inexpensive to manufacture unlike gas turbines and use inexpensive fuel, and drive the same electrical generator without the need for auxiliary units. Thus, the thrusters a complement the wind power when needed. Consequently, a community will be assured of certain level of electrical power at all seasons at low capital investment.
In a third instance, as another feature of the present invention is a method of recycling kinetic and thermal energies to produce electrical power. This includes utilization of dynamic compression of ambient air through an inlet, further compounding pressure build up through a compressor or a centrifugal fan and capturing thermal energy while cooling the armature in a heat exchanger. Alternators at full load produce heat resulting from iron and copper (I2R) loses. This loss generally amounts to about 10 to 15% of generated power. To recycle this heat a heat exchanger will be used. The present invention proposes to use ambient air as the cooling medium in the heat exchanger. The hot air after passing through the heat exchanger is diverted through an air duct in the blade, where it is compressed due to centrifugal acceleration and finally injected into the combustion chamber of the thruster. In the combustion chamber it mixes with incoming ram air and the fuel. The mixed gas is burnt in the combustion chamber and expanded through an expansion nozzle to produce thrust. Thus, the kinetic energy of the incoming air and the thermal energy of the armature is transformed into electrical energy.
Other and further features, advantages, and benefits of the invention will become apparent in the following description taken in conjunction with the following drawings. It is to be understood that the foregoing general description and the following detailed description are exemplary and explanatory but are not to be restrictive of the invention. The accompanying drawings which are incorporated in and constitute a part of this invention, illustrate one of the embodiments of the invention, and together with the description, serve to explain the principles of the invention in general terms.
The foregoing aspects and other features of the present invention are explained in the following description, taken in connection with the accompanying drawings, wherein: